The buck voltage converter is a conventional type of converter which employs an inductor series with a switching regulator where simplicity, high efficiency and the use of miniature output filter components are desirable advantages. The inductor is coupled to the load resistor, and an output filter capacitor is coupled across the load resistor. In addition, at the opposite end of the inductor, a diode is connected in shunt across the capacitor and the load resistor to permit continuous current conduction through the inductor when power switch is turned-off so that the diode receives the current generated by the collapse of the electromagnetic field of the inductor.
In this type of circuit, the steady state output voltage is directly dependent upon the input voltage and the duty cycle, and is independent of the load current. Although load regulation is inherently good, a higher than desirable ripple occurs, however, which appears in the output current, due to the switching frequency harmonics of the current that is drawn from the input line. Also, when the load changes, this type of circuit tends to have a relatively slow response to a change in the load.
FIGS. 1 and 2 illustrate the operation of a prior art circuit of the type generally described above. The DC input power source 12 is connected to the terminal 14 of the switch 18, which may be any type of suitable switch including a transistor switch, which is used to complete the path between the terminal 14 and the cathode of the diode 20 when the switch is closed. The anode of the diode 20 is connected to the common side of the input power source 12.
An iron-cored inductor 22 is connected in series with the switch 13 between the cathode of the diode 20 and plate of the capacitor 24. The other plate of the capacitor 24 is connected to the anode of the diode 20. A load resistor 26 is coupled in parallel across the capacitor 24. The output current I.sub.OUT, which flows through the inductor 22, is illustrated by the waveform of FIG. 2.
The present invention, by using two inductors in a dual-inductor, buck-switching topology, with two commutating switches that are switched at a duty cycle greater than 50%, greatly reduces switching harmonics, and thereby supplies an output load current that has much less ripple than the Prior Art supply. In addition, the two inductors allow the circuit to respond more quickly to large load transients.